The presence of ferromagnetic particles in the oil flow of a lubrication system such as the gearbox of a gas turbine engine is an indication of distress in the bearings and gears of the gearbox and engine which if not corrected could result in a catastrophic failure. A chip detector is an electrical device used to detect the buildup of such particles. Hobble, U.S. Pat. No. 4,008,464 discloses a typical chip detector comprised of two, spaced apart, annular magnets mounted on a common insulating member. Each magnet is discretely wired to an indicator circuit. As the oil flows over these magnets, ferromagnetic particles are captured by the flux lines between the magnets. When a sufficient number of particles have been captured, the gap between the two magnets is bridged to provide an electrical conducting path the resistance of which is low enough to permit electrical current to pass and actuate a warning light. The combination of magnets, and conductor to form a single chip gap is generally referred to as a chip element.
Some gearboxes have a plurality of adjacent oil flow paths each fluidly isolated from the other, and each requiring its own chip element. To meet this requirement, multiple element chip detectors have been built that have a plurality of chip elements radially stacked about the longitudinal axis of the detector so that the chip gaps are parallel with this axis. An insulating member is mounted between each of the chip elements to both electrically isolate each of the chip elements from ground and to prevent oil from leaking from one flow path to another.
A major disadvantage of these multiple element chip detectors is that they require a multiplicity of conductors, magnets and insulators as well as separate circuitry for each chip element.
Accordingly, there is a need for a simpler, multiple element chip detector that for a given number of flow paths has fewer parts and only a single electrical circuit.